In posting questions on MSE, I find that, if a question is not answered within a day or so, it will not receive an answer at all. Typically, I have waited for several weeks before cross-posting such a question on MathOverflow, where usually it gets a good response. From my experience, however, there seems to be no point in waiting so long, and a wait of one week is plenty to confirm that a question will not be answered.

I normally post a question on MSE first because I expect or hope that it will get an answer here. Sometimes it turns out that a question is more suited to MO, but generally I can't tell this in advance—perhaps there is a ready answer that I missed, and I don't want to bother the MO forum with off-topic material.

Thus, to formulate a specific question: Is it is considered acceptable behaviour to post on MO a question that received no answer on MSE within a week? If not, what would be deemed an appropriate waiting period?

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    $\begingroup$ I have added the (cross-posting) tag. Since you're interested mainly in MO, maybe (mathoverflow) could be added as well. Using those tag, you can check some older discussions related to this topic, if you check the questions tagged cross-posting or cross-posting+mathoverflow. $\endgroup$ Commented Sep 18, 2020 at 13:23
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    $\begingroup$ You might have a look at some posts on this on MathOverflow Meta, such as: Cross posts to Math SE. And also on this meta: Asking the same question on MSE and MO. (Some of the questions linked there might be of interest, too.) $\endgroup$ Commented Sep 18, 2020 at 13:26
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    $\begingroup$ I recommend a week, during normal (non pandemic) times. Then those who read math.se only once a week have a chance to answer. Of course your question must have good tags, so our hypothetical reader will see it even if it is not on the "recent" page. $\endgroup$
    – GEdgar
    Commented Sep 30, 2020 at 12:08

2 Answers 2


Thanks to the helpful links posted in the comments by Martin Sleziak, I obtained a precise answer to the question here. The answer, on MO Meta, was to a question about cross-posting in the opposite direction, but it explicitly dealt with both directions.

The answer, which was the sole answer to the question and by a high-rep poster, was well upvoted and accepted. In short, it said that one week is fine, and I will take that advice.


Please do not post the same question on multiple sites. See the general rules on Meta.SE: Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?.

These rules are the default for Stack Exchange sites. Individual SE sites can set a local policy that overrides that default, if they wish. If both sites allow cross-posting, then you may cross-post as long as you comply with both sites' rules. Otherwise, do not cross-post your question on multiple sites -- no matter how long you wait.

Math.SE's policy appears to be documented here: Is cross-posted forbidden/discouraged on Stack Exchange sites? If so, why? and Is cross-posting the same question to multiple sites not allowed when it is on-topic everywhere? and Asking the same question on MSE and MO. Before cross-posting on another site, please make sure you find their policy on their Meta. If you can't find a specific policy on their Meta that allows cross-posting, then do not cross-post; the general default SE policy applies, and cross-posting is forbidden.


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